Melt initiation and mantle exhumation at the Iberian rifted margin: Comparison of pure–shear and upwelling-divergent flow models of continental breakup

Observations of a wide (up to 170 km) zone of exhumed continental mantle on the Iberian non-volcanic rifted margin have questioned our understanding of the processes involved in continental breakup and seafloor spreading initiation. Models of continental lithosphere thinning by pure–shear predict melt generation before continental breakup, and thus do not predict the exhumation of mantle. Whilst the paucity of volcanism during breakup on the Iberian margin may be explained by invoking a cooler or depleted mantle, or by poor melt extraction, other lithosphere scale processes may play an important role during continental breakup. We compare melt production predicted by pure–shear models of continental lithosphere thinning to that predicted by an upwelling–divergent flow model, using kinematic constraints appropriate to the Iberian margin. The upwelling–divergent flow model predicts exhumation of a more than 50 km-wide zone of continental mantle prior to melt initiation, and we suggest that this mode of lithosphere deformation may play an important role in the formation of rifted margins.